1. Field of Invention
The present invention relates to a document surface micro-adjust mechanism. More particularly, the present invention relates to a micro-adjust mechanism for adjusting the distance of separation between the document surface and the lens of an optical scanner.
2. Description of Related Art
Due to great advances in the functions of computers and the rapid proliferation of networking and multimedia communication, image patterns or documents are often directly captured by a digital camera or indirectly through an optical scanner and converted into digital data files. The images in the data files may be identified, edited or stored and later displayed through a computer monitor or other electronic product.
According to the manner in which document image is input, optical scanners may be classified into palm top scanners, paper feed scanners, drum scanners, and platform scanners. The palm top scanner operates by manually moving the scanner over the surface of a scan document horizontally. The paper feed scanner operates by putting a scan document at the entrance of a paper feeder. The paper feeder moves documents into the scanner one at a time so that scanning is performed at a stable and uniform speed. The platform scanner has a flat transparent panel for placing a scan document. An optical system underneath the flat transparent panel moves so that the scan document is scanned one section at a time. Note that since a platform scanner is capable of scanning a B5 size document or bigger, a rather large total trace (TT) is required to project the image of a large document onto a sensor having a smaller width.
Following progressive maturity of manufacturing technique for optical scanners, different types of optical scanners are developed to deal with different types of documents. To scan a card or a picture, there is no need to have an optical scanner with a large total trace (TT). In general, to scan a small document, an optical scanner often employs a roller to drive the document forward while an optical system scans the moving document. This type of scanner occupies a smaller space. A scanner of this type is referred to as a card scanner if cards are the main scanning items and a photo scanner if photographs are the main scanning items.
FIG. 1 is a schematic cross-sectional view of a conventional small document optical scanner. As shown in FIG. 1, the scanner 100 comprises a casing 110, a transparent document platform 112, a roller 120, a light source 130, a group of reflecting mirrors 140, an optical lens 150 and a sensor 160. A document 10 driven by the roller 120 is fed onto the document surface 114 of the transparent document platform 112. The document picks up light from the light source 130 and reflects a portion of the light back along an optical path 20. The light reflects repeatedly through the group of reflecting mirrors 140 to enter the optical lens 150. The optical lens 150 focuses and projects the light onto the optical sensor 160. On receiving the light, the optical sensor 160 converts the image pattern on the document 10 into digital output signals.
After all the components of the optical scanner 100 are assembled together, minor adjustment is often made through the optical lens 150 along the optical path 20. The optical lens is moved so that light reflected from the document 10 is focused precisely on the sensor 160. FIG. 2 is a schematic diagram showing minor adjustment of the optical lens to focus an image on a sensor. Note that the document surface 114 and the sensor 160 (image surface) are fixed relative to each other. Only the optical lens is shifted to bring the light from the document 10 at the document surface 114 exactly in focus on the sensor 160. The optical lens is fixed in position after adjustment.